Electrical testing instrument



Sept. 2 1924. I 1,506,792

c. w. TERRY ELECTRICAL TESTING INSTRUMENT Filed April 1, 1920 awuemioz Ch'aries 71/ 2 61"? ll eteuted Sept 2, llQ'Z lO GHARLE$ TERRY, 0F DETRQE'I, MICHIGAN, AESIGNGR, BY MESNE ASSIGNMENTS,

TU HYRATE MANUFACTUR1NG COELZ MTY, A GQ'E'EURATION @31 ELEGTR'LGAL TESTING WSTEUMENT.

Application filed April 1;

To aZZ whom it may concern:

Be it known that l, CHARLES l/V. TERRY, o citizen of the United States of America, residing at Detroit, in the county of Vll'eyne end-State of Michigan, have invented certoiii new and useful Improvements in Else-- tricel Testing" instruments, or which the -following is e specification, reference be had therein to the accompanying drow- 1G logs.

The invention relates electrical testing instruments and it is the object of the invena construction particularly so in testing sud detecting ions electric sys- It is with 3 systems provide storage for charging the some,

'ing the orig: e, i 'oition sud other elements e to hettery 'iclri easily circuit and iug connecere mode,

' itiou conretter set to "ore s comectir s by my inst ument 7 A is o or cesiur: containing eleciustrumeut B, heviug the usual move LB index heed C cooperescele llu couuuou ell 1920. serial No. 370,457.

such instruments the indication is dependout upon the resistance of e shunt, through which a portion of the current is deflected. Inasmuch, however, as the current in the system varies greatly, depending upon the particular operation or the articular device which is iii use, it would he impossible to make all of the verious tests with an instrumeut having it shunt of unvsryiug resistance. Also, if the resistance of the shiuit weresufiicieutly high for making certain tests, there would be great danger of burning out the instrument in rushing tests; While, on the other heed, it the resistence were sufficiently low for tests, there would he little or no indication the former. 3 improved instrument It overcome the duuculty by providing shunt ehle Q resistance, together wi h recess for holding the resistance low, While permitting e .porery o increased resistance,

in detail, is e horse hoe ing the segmeutel pole bracing so. armature F, I isattached G 21115 rial connector preferahi insulated cable, and Whi from the casing A, being p'referehi vided their ends with spring H for quick .I. r .J, T ettechmeut with the cstteiy i 4. t. v W, "5. terminals or other part oi the systel ll.

is e shunt connection of relativel low resisteuce which extends hetweeu the COI1i16- tors-G end G end which as sho -"r comprises the terminal blocks 1, I so the resistor hers I exteud ue therehetweeii. Between the hloclrs l and I there are dumher of the hers I in parallel, so as low electrical resistance, but between the hloclrs 1 end I there hut e si le her having therefore e higher electrical resist once; The leads Gr end C ere sttechod, re; spectively, to the hlochs l and l end the Wt loloelr 1 is normally in electrical coutect with the hloclr P, so that the current'ceupess through a l of the hers i in parallel, There is, however, providede device for seperetiug the blocks ll rm 1 to compel the current o puss through the single her I this consisting of e lever J spore" by e push loutt-ou d and ectuetiug e pm ing through an aperture the hlo pressing the hie-ch has an insulated lower end, so that when pressure is brought to bear the blocks I and I will be both mechanically and electrically separated.

In use, the leads G and G of the instrument are connected into the main circuit,

preferably by disconnecting one of the bat- J, this operating through the lever J and pin J will separate the blooks I and I so that the resistance of the shunt is increased many times. This enables the instrument to be used for measuring currentsof smaller volume, but the high resist: ance is in circuit only as long as the but-ton is pushed down and when this'is released, the low resistance is automatically cut in. Therefore, it would be impossible for the operator to carelessly injure the instrument by leaving in the high resistance when there is a large current volume in the circuit.

lnthe tests thus far described the instru-- ment is used as an ammeter, but thereare various other tests which it is desirable to make in connection with motor vehicle electric systems. To adapt the instrument for these tests it is provided with a series of binding posts K, etc., to which connections may be led from various parts of the system.

A switch L is arranged at one side of the instrument for changing the instrument from the main circuit to the binding-post circuits.

Some of the specific tests which can be made are as follows: To test the battery current, after the instrument is connected into the main circuit, as before described,

the starting switch M' is closed so that the current from the battery N will flow through the instrument andthe starting circuit, including the starting motor 0. A double set of indlcations are laced in connection with the scale and which are respectively used for the low resistance and high resistance shunts. Thus, in,testing the starting current, the low resistance shunt being used, readings can be taken from zero to three hundred amperes. When the engine starts and the starting switch M is opened, the current from the generator P will flow through the main circuit, but thisis too small in volume to be measured by the low resistance shunt. The operator, therefore, resses the button J, which throws in the iigh resistance shunt, and readings can then be taken on the same scale from zero to thirty amperes.

v The instrument'may lm converted into a .volt meter by turning the switch L and may then be used for testing the generator, lights, horn, etc. Suitable additional markings are placed in connection with the scale for use in these tests.

What I claim as my invention is:

An electrical testing instrument comprising a casing, a pair of terminals in said casings, a metering device connected between said terminals, leads extending from said casing for coupling said terminals into a circult, a resistor bar extending between said terminals, a third terminal arranged to contact with one of said terminals, a series of resistor bars extending between said third terminal-block and the other of said pair of terminals, and manually operable means for electrically disconnecting said. third terminal block from said first terminal thereby disconnecting said series of resistance bars, and resilient means for automatically connecting said third and first terminals upon releasing said manually operable means.

In testimony whereof I .aflix my signature CHARLES W. TERRY 

